In order to determine the properties of a particular formation, a core sample may be extracted. For instance, a vertical or horizontal hole may be created in a formation. A column of rock or other materials found in the formation may be extracted as the hole is made, and then removed from the hole, after which a detailed study may be performed. The detailed study and analysis may yield information and identify the lithology of the formation. Other characteristics such as porosity and permeability of the formation, the potential storage capacity and/or production potential for hydrocarbon-based fluids (e.g., oil and natural gas), and the like may also be determined from the core sample.
Example coring systems may attempt to extract the core sample in a state that, to the extent possible, closely resembles the natural state in which the rock and other materials are found in the formation. For instance, a coring bit may be coupled to a drill string and extended into a hole, such as a wellbore, borehole or other subterranean tunnel. The coring bit may include a central opening or aperture and, as the coring bit rotates and drills deeper into the formation, materials from the hole can enter through the central opening and form a column of rock in the drill string. When the column is sufficiently long, the column of rock may be retrieved and brought to the surface.
The column of rock forming the core sample may form directly within the drill string, and then be returned to the surface by lifting the coring bit towards the surface. In other systems, a core barrel may be lowered through the central opening in the drill string. A column of rock can form in the core barrel, and the core barrel can be retrieved. Another core barrel may then be lowered through the drill string and used to obtain another core sample from the drilled section of the formation.